This is a link to an article from Harvard Medical School Publications (one of my favorite e-publications) about how laughter and joy can positively impact your health. Note that the other side of things i.e. anger, depression, and stress will have a negative impact on your health and well being.
http://www.facebook.com/l.php?u=http%3A%2F%2Fbit.ly%2FgnoEXE&h=4f86a